Investigation Of Dehydration Of SAGD Produced Ultra-heavy Oil Under High-frequency Pulsed Electric Fields

With exploitation of oil fields having entered later period and polymer flooding method been widely used,the inferior and emulsification of crude oil become more and more seriously,as a result,the pre-treatment difficulty of crude oil has been greatly increased.Recently,the steam-assisted gravity drainage(SAGD)has been widely utilized in industry.The ultra-heavy oil is rich in suspended solids,colloid and asphaltene,and“space steric”effect is significant due to the existence of small solid particles,making the deep dehydration of produced liquid quite difficult.Although high-voltage pulsed electric field can significantly improve the efficiency of demulsification,it has not yet been successfully applied to deep dehydration of ultra-heavy oil.Based on the Electrohydrodynamics(EHD)theory,this paper conducts multi-scale experiments,numerical research and theoretical analysis on the high-voltage pulsed electrocoalescence of SAGD produced ultra-heavy oil and modelling oil emulsion to find the appropriate pre-treatment and deep dehydration approach and set up the process flow diagram.Firstly,numerical work is conducted to investigate droplet deformation and droplet-droplet coalescence in SAGD produced ultra-heavy oil at 120 ~oC.The results show that,at high frequency(3000 Hz),the droplet deformation process is independent on the pulsed electric fields.With increasing acting time,the deformation increases rapidly firstly and then slowly increase to a semi-stable state with slight fluctuations.The deformation process of high-frequency pulsed DC electric field is similar with that of constant DC electric field.The influence of electric field parameters(electric field strength,electric field frequency and duty ratio)and physical parameters(initial droplet size,bulk viscosity,droplet angle and droplet centre distance)is significant on droplet-droplet coalescence.Secondly,based on the investigation of the basic physical parameter(viscosity,density and water content)of SAGD produced ultra-heavy oil,this paper reports the influence of surfactant on the pre-treatment process and illustrates the influence of electric field parameters(electric field strength,electric field frequency and duty ratio)and operating parameters(acting time and operating temperature)on the electro-dehydration of SAGD produced ultra-heavy oil.The results show that the dehydration efficiency increases firstly and then decrease with increasing electric strength,electric frequency and duty ratio,respectively.In addition,the dehydration efficiency increases firstly and then decreases with increasing operating temperature,as well.Finally,dimethyl silicone oil is used as the continuous phase to investigate the influence of impurity components(salt,surfactant,pH of dispersed phase,and solid particles)on dewatering efficiency of SAGD modelling oil emulsion,based on which the appropriate pre-treatment and deep dehydration approach and the process flow diagram is obtained.The experimental and numerical work and theory analysis work above lays a good foundation for further research on demulsification mechanism of SAGD produced ultra-heavy oil.The outcome of this work is potentially useful for optimising the design of compact and efficient oil-water separator.